1. Field of the Invention
The present invention relates to a plasma-assisted processing system and a plasma-assisted processing method that produce a plasma by using the energy of a high-frequency wave, such as a microwave, and use the plasma for processing a substrate, such as a semiconductor wafer.
2. Description of the Related Art
A semiconductor device manufacturing process includes a step of processing a semiconductor wafer (hereinafter referred to simply as xe2x80x9cwaferxe2x80x9d) by using a plasma. FIG. 16 shows a known microwave plasma-assisted processing system that carries out a plasma-assisted process. As shown in FIG. 16, the microwave plasma-assisted processing system has a vacuum vessel 9 provided with a stage 91 for supporting a wafer W thereon, a planar slot antenna 92 disposed in a ceiling region of the vacuum vessel 9, a microwave power unit 93, a coaxial waveguide 94 provided with a shaft 94a and connected to the microwave source 93 and the vacuum vessel 9, a microwave transmitting plate 95 of quartz, and a gas supply unit 96. A microwave generated by the microwave power unit 93 is guided through the waveguide 94, the antenna 92 and the microwave transmitting plate 95 into the vacuum vessel 9, a process gas supplied by the gas supply unit 96 into the vacuum vessel 9 is ionized by the microwave to produce a plasma, and the plasma is used for forming a film on the wafer W or for etching a film formed on the wafer W.
A plasma is a complicated combination of electrical, physical and chemical phenomena and its mechanism has many points which have not yet been elucidated. As matters stand, the dependence of the condition of a plasma on process conditions has not been definitely elucidated. Therefore, even if a highly uniform plasma can be produced under certain process conditions including pressure and power of a microwave, sometimes, the uniformity of the plasma is deteriorated under other process conditions.
The uniformity of a plasma is reflected directly on the uniformity of a film thickness or the uniformity of etch rate. Since the recent semiconductor devices are miniaturized and are provided with thin films, the yield of semiconductor devices is greatly dependent on the uniformity of the plasma. Accordingly, the development of techniques capable of producing a highly uniform plasma regardless of process conditions has been desired.
It is an object of the present invention to provide a plasma-assisted processing system and a plasma-assisted processing method capable of producing a highly uniform plasma and of processing a substrate in a high intrasurface uniformity.
According to a first aspect of the present invention, a plasma-assisted processing system comprising a vacuum vessel internally provided with a stage, a high-frequency wave transmitting plate attached to the vacuum vessel, a planar antenna disposed opposite to the high-frequency wave transmitting plate, and a high-frequency power unit that sends a high-frequency wave for producing a plasma to the antenna, and capable of propagating a high-frequency wave for producing a plasma through the antenna and the high-frequency wave transmitting plate into the vacuum vessel, of producing a plasma by ionizing a processing gas supplied into the vacuum vessel by the energy of the high-frequency wave and of processing a substrate mounted on the stage in the vacuum vessel by using the plasma; comprises: a lifting mechanism that moves the antenna vertically relative to the vacuum vessel; an electromagnetic shielding member surrounding a region between the antenna and the high-frequency wave transmitting plate; a level estimating unit that estimates a level of high-frequency wave cutoff density formed between the high-frequency wave transmitting plate and a plasma producing region; and a controller that controls the lifting mechanism to adjust the level of the antenna so that a cavity of a proper size for the high-frequency wave is formed between the antenna and the level of a cutoff density for the high-frequency wave for producing a plasma.
Since the lower end of the cavity for the high-frequency wave can be known, the level of the antenna can be properly adjusted on the basis of the result of operation of the level estimating unit by determining the proper size of the cavity beforehand.
According to a second aspect of the present invention, the level estimating unit includes a transparent plate covering an opening formed in a side wall of the vacuum vessel, and a cease region detecting unit capable of optically detecting a lower limit level of a cease region in which a plasma produced in the plasma producing region ceases between the high-frequency wave transmitting plate and a region in which the plasma is luminescent, and the level of the cutoff density is estimated on the basis of the detected lower limit level for the cease region.
According to a third aspect of the present invention, the level estimating unit includes a high-frequency wave radiating unit that delivers a detecting high-frequency wave from above the plasma to the plasma, and a high-frequency wave receiving unit that receives the detecting high-frequency wave delivered to and reflected by the plasma, a level of the cutoff density for the detecting high-frequency wave is determined on the basis of a position of the reflected high-frequency wave on the high-frequency wave receiving unit, and a level of the cutoff density for the plasma producing high-frequency wave is estimated on the basis of the level of the cutoff density for the detecting high-frequency wave.
Although the level of a cutoff density for the plasma producing high-frequency wave and the lower limit level of the cease region are different from each other, the difference between those levels can be regarded as substantially fixed. Therefore, those results of detection can be used in substitution for the level of a cutoff density for the plasma producing high-frequency wave. Estimation of the level of a cutoff density for the high-frequency wave includes the use of the detected lower limit level of the cease region of the plasma and the detected level of a cutoff density for the detecting high-frequency wave as substitutes, and includes the estimation of the level of a cutoff density for the plasma producing high-frequency wave on the basis of a predetermined algorithm.
According to a fourth aspect of the present invention, a plasma-assisted processing system comprising a vacuum vessel internally provided with a stage, a high-frequency wave transmitting plate attached to the vacuum vessel, a planar antenna disposed opposite to the high-frequency wave transmitting plate, and a high-frequency power unit that delivers a high-frequency wave for producing a plasma to the antenna, and capable of propagating a high-frequency wave for producing a plasma through the antenna and the high-frequency wave transmitting plate into the vacuum vessel, of producing a plasma by ionizing a processing gas supplied into the vacuum vessel by the energy of the high-frequency wave and of processing a substrate mounted on the stage in the vacuum vessel by using the plasma; comprises: a lifting mechanism that moves the antenna vertically relative to the vacuum vessel; an electromagnetic shielding member surrounding a region between the antenna and the high-frequency wave transmitting plate; a storage unit that stores set antenna levels for recipes for plasma-assisted process; and a controller that reads a level of the antenna for a selected recipe from the storage unit and controls the lifting mechanism to adjust the level of the antenna.
According to a fifth aspect of the present invention a plasma-assisted processing method comprises the steps of: propagating a plasma producing high-frequency wave delivered by a high-frequency power unit through a planar antenna and a high-frequency wave transmitting plate into a vacuum vessel; producing a plasma by ionizing a processing gas supplied into the vacuum vessel by the energy of the high-frequency wave; and processing a substrate supported on a stage disposed in the vacuum vessel; wherein the substrate is processed by a plasma-assisted process after adjusting the level of the antenna relative to the vacuum vessel so that a cavity region of a proper size for the high-frequency wave is formed between the antenna and a level of a cutoff density for the high-frequency wave in the vacuum vessel.